Degreasing process



Patented Mar. 20, 1945 nnoaansmc PROCESS Wilbur H. Petering, Metuchen,and Adam G. Aitchison, Westfield, N. J., assignors to West--, vacoChlorine Products Corporation, New York, N. Y. a corporation of DelawareNo Drawing. Application December 28-, 1943,

Serial No. 515,990

9 Claims. ('01. 134-31 solvent, so that the article brought into contactH with thesolvent vapor will have a suificiently low temperature tocause the desired condensation of This invention relates to animprovement in degreasing processes and other processes whereinchlorinated solvents are used as solvent media. It comprisesparticularly a method of degreasing articles with surfaces of a metalhaving a decomposing efiect on chlorinated grease solvents, such asaluminum goods, wherein grease is removed from such a metal surface by achic-.

rinatedsolvent of a type normally subject to,

such decomposition, containing a minor amount of certainoxygen-containing organic compounds, advantageously esters, whichrestrain such decomposition.

This application is a continuation-in-part of our co-pendingapplication,

386,544 filed April 2. 1941.

.The removal of grease films from metal sur- Serial Number solventonitsfsurface in the vapor. chamber.

, As'noted, numerous solvents have, been em ployed in degreasingoperations. .nmongthese, solventsofv thechlorinated hydrocarbon type,

including both saturated, compounds such as carbon tetrachloride,ethylenedichloride, et cetera,

and unsaturated compounds such astrichlorethylene, perchlorethylene, etcetera, have been widely employed because of their high greasesolventcapacity and their low inflammability.

' Several of these chlorinated compounds are confaces by the applicationof grease solvents has been widely practiced during recent years.Numerous solvents have been employed, and numerous variations of thedegreasing procedure have been suggested. In one method of operating,the metal article to be degreased is brought into contact with thesolvent in the liquid phase. This may be accomplished by immersing thearticle in a large body of the solvent, or by spray- ,ing the solvent onthe surface of the article. In

another common method of degreasing, known generally as vapor-phasedegreasing, a body of solvent is maintained atthe boiling point and in 1communication with a chamber adapted to contain a large body of thesolvent vapor. The

article to be degreased is brought into contact with this body of vapor,and causes condensation of the solvent on the greasymetal surface. Thecondensed solvent removes grease and oil from the metal surface anddrips off, usually returningto the boiling body of the solvent. With itgoes dirt, adheringto the greasy surface. This dirt often includes metalchips. In vapor-phase degr easers of this type, it is conventional toprovide cooling coils or some equivalent arrangement near the top of thesolvent vapor chamber to prevent or minimize the escape of vapors andloss of solvent from the system. Solvent condensed by such cooling coilsis generally substantially uncontaminated by either grease or dirt, andis usually returned to a clean solvent.

reservoir, which, in many cases. is arranged to overflow into the"solvent boiling compartment.

In some cases, even when employing vapor-phase degreasing, the articleto be degreased is preliminarily dipped in a body of liquid solvent.When hot solvent is employed for-this purpose. there is sometimes asubsequent dip in cooler sidered non-inflammable. Of the availablesolvents of this type, trichlorethylene-is probably most widely used indegreasing. However, it is seldom used without the addition of some(stabilizer, adapted to prevent or retard its decomposition duringstorage and normal use. This so-called normal type of decomposition ispromoted by light and oxygen. The actionof light and oxygen isaccelerated by heat. Several stabilizers are available and commonlyusedfor the purpose of inhibiting this decomposition.

These previously known stabilizers are, efiective when present in minuteamounts in preventing decomposition "of trichlorethyleneand otherdegreasing solvents during storage and during the usual degreasingoperations applied to, ferrous metals and several other metals. However.

when the metal to be degreased is aluminum or analuminum alloy, it hasbeen found that a different type of decomposition of the solvent isencountered, and that this type of decomposition may occur even in thepresence of stabilizers which are effective in all other cases. Thisform of decomposition. of chlorinated solvents in contact with metallicaluminum ,or its alloys is evidenced by a rapid rise in acidity (largelyhydrochloric acid by pronounced discoloration of the solvent, and, inthe advanced stages of decomposition, by the formation of a tarry orgummy mass in the solvent.

Efforts have been made heretofore to eliminate or minimize this type ofdecomposition by various special practices. these practices have beenpartially successful, in that they have reduced formation of theabovementioned tarry and gummymasses, in the solvent. However. when suchresults have been obtained, they have been accompanied bydudesirable'results of other types. such as increased It does not appearthat prior, to this invention there has been any satisfactory,

acid development.

In some instances,

' acid and otherdeleterious decomposition products, is prevented by. theaddition to the chlorinated hydrocarbon solvents of certainoxygencontaining organic compounds such as organic esters.

The organic esters have many advantages for the present purposes. First,as a class, they are usually soluble in chlorinated hydrocarbons and arecompatible with such solvents under service conditions. Underordinary'conditions they do not react with the chlorinated hydrocarbonsto form sludge or other deleterious by-products'. Likewise, the estersdo not attack metals. They are inexpensive and have boiling pointscovering a wide range which permits selection 01' an ester having aboiling point near that or the solvent to be stabilized.- In otherwords, the esters efl'ectivelystabilize chlorinated hydrocarbons against"metal-induced decomposition without any deleterious'actio'n, bothduring storage and under service conditions. The following esters areillustrative oi the types that are efl'ective in the practice of ourinvention:

Ester Formula 1. N-hutyliormatc H oicnmcm .2. Ethyl acetate CHIC I I V.0cm

' l o :i. Isopropylsostate CHIC ocmcnm 4. Amylsoetatc 0E|O\ I 00:31.

OCH! 6. Dlmethylcarbonste 0=='C\ OCH:

7 001K! 6. Trlethylortho iormaie HC-Othm 0 0 7. Dimethyl oxalateGHQ-EL-PL-OCH:

OCH:

8. Trimothylotthoaostate CHE-OCH:

0 I 9. Diethyl oxalate H;C:OECOCQH| 0 H H g 10. Ethylmaloneie C-g--0C;H|

alls solution to the problem of decomposition en- Ester Formula II C-OCsHl 11. Ethyl benzoste ll C0 CHSCHCHI l2. p-Amino isobutyl benzoate Hav o is. n-Butyl enz me en orsin -00in.

where B: may be hydrogen or an organic radical such as an aliphatic,aryl, heterocyclic or alicyclic group and R: may be an organic radicalsuch as 'an aliphatic, aryl, heterocyclic or alicyclic group.

These radicals may contain other substituents. The esters of orthoacids, esters of carbonic acid and esters of diand multi carboxylicacids may also be used.

In the case of esters prepared from aliphatic employ a wide variety ofesters as noted above.

These oxygen-containing compounds are generally employed in minoramounts, advantageously in the order 01' 1 per cent of the amount ofchlorinated solvent by weight. However, as the efl'ectiveness 01 thesestabilizers varies to some extent with the type of compound employed,the particular percentage incorporated in the chlorinated hydrocarbonsolvent may be varied to obtain the stabilization desired. Ordinarily itis advantageous to add definite molar percentages of the esters to thechlorinated hydrocarbon solvents. Howevenfor purposes of the presentinvention, the more ester present, the most eilective the composition inrestraining this "metalinduced" decomposition. This seems to be truebecause these oxygen compounds unite chemically with the aluminumcompounds that appear to cause the metal-induced decomposition and thusthe more ester present the more stabilization obtained. For"metal-induced decomposition claimed in this application it is generallyadvantageousto use about 1 mol of oxygen compound per 99 mole oi'chlorhydrocarbon. However, this amount may be increased withproportionately greater stabilization against metal-induceddecomposition.

Inthe practice of our invention, many and variousembodiments thereof maybe employed. For instance, the chlorinated hydrocarbon solvent, inaddition to the stabilizers described, may also contain one of the knownstabilizers against norchlorinated solvent and the finely divided maldecomposition, as previously mentioned, such as aralkyl ethers ofhydroquinone, described in Pitman Patent 2,319,261.

One specific advantage resulting from the addition of suitable esters tochlorinated de greasing solvents, as described hereinabove, is that thepresence of a minor amount of the ester with the resulting decrease inmetal-induced decomposition, permits operation of the degreasingequipment for a. longer period without the necessity of shutting down toclean out accumulations in the boiling compartment. As previously noted,the reactions involved in this metalinduced decomposition are somewhatobscure. One explanation of these reactions is that the accumulation ofnon-volatile oils removed from the work during the degreasing operation,may raise the boiling point (or range) of the liquid in the boilingcompartment of the degreaser to such an extent that reaction sets inbetween the aluminum or other metal which has also been washed off thework. This waste metal accumulating in the liquid solvent has largeeffective surface areas which are highly reactive, especially at theincreased boiling temperature of the dirty solvent. It may be that thelarge metal surface catalyzes the decomposition, or it is possible thataluminum chloride forms at the surface of the metaland that thiscompound is the active decomposing agent.

Whatever the mechanism of the metal-induced decomposition, it has beennecessary to remove the accumulation of oily material and finely dividedmetal and metal compounds from the boiling compartment at frequentintervals. This involves additional labor, loss of production during thecleaning period, and loss of solvent. These diificulties are largelyeliminated by operating in accordance with the present invention, and ithas been found that a vapor-phase degreasing unit can be kept inoperation when degreasing aluminum, for example, up to at least threetimes fore, when suitable oxygen-containing organic compounds are addedto the solvent, as described hereinabove.

Similar advantages are obtained in liquidphase degreasing operations inwhich hot chlorinated solvents are employed.

In a specific example illustrative of a useful embodiment of the presentinvention, a degreasing solvent was prepared containing 99.0 parts byweight of stabilized trichlorethylene, and 1 part by weight of isopropylacetate. This solvent was used in a vapor-phase degreasing operation ofthe type previously described for degreasing aluminum surfaces. Noobjectionable decompositionwas encountered, even after continuing theoperations without cleaning out the boiling compartment of the degreaserfor considerably longer than had been possible before the use of theester in accordance with this invention.

These chlorinated solvents, such as trichlorethylene, containing minoramounts of organic in the, past as long as was permissible heretoesters,are particularly adapted for use in degreasing aluminumand its alloys.Such solvents are also useful in degreasing other metals, including zincand magnesium and their alloys as well as iron, steel, copper, etcetera.

- While we have particularly described our invention hereinabove withrespect to certain organic esters, it will be obvious to the skilled inthe art that the invention is not limited to the specific examplesshown, but may be practiced and embodied within the scope of the claimshereinafter made. I

What we claim is:

1. As an improvement in degreasing surfaces 1 of aluminum and its alloyswith chlorinated hydrocarbon solvents normally subject to deteriorationin the presence of aluminum, the improvement which comprisesmaintaining, in admixture with such chlorinated solvents, a minor amountof a carboxylic acid ester to inhibit such metal-induced decompositionthereof.

2. The method of claim 1, wherein said chlorinated hydrocarbon solventis trichlorethylene.

3. The method of claim 1,wherein said chlorinated hydrocarbon solvent isperchlorethylene.

4. The method of claim 1, wherein the ester ,is an aliphatic esterprepared from an aliphatic carboxylic acid having less than six carbonatoms and an aliphatic alcohol having less than six carbon atoms.

5. The improved process for degreasing surfaces of metals of the classconsisting of aluminum and its alloys having a decomposing effect onchlorinated hydrocarbon grease solvents, which comprises establishing abody of grease solvent in communication with a space adapted to receivevapors therefrom, said solvent comprising a major proportion ofchlorinated hydrocarbon solvent, normally subject to decomposition inthe presence of such metal surfaces,

and a minor proportion of a carboxylic ester.

having the property of restraining decomposition of such solvents in thepresence of said metal surfaces, boiling said body of grease solvent andthereby maintaining a body of vapors thereof in said vapor space,contacting the metal surface to be degreased with said body of vaporsand returning the solvent condensed by said metal to said boiling bodyof solvent, the amountof said' ester in said body of grease solventbeing sufflclent to inhibit metal-induced decomposition thereof.

6. The method of claim 5, wherein the chlorinated hydrocarbon solvent istrlchlorethylene.

7. The method of claim 5, wherein the chlorinated hydrocarbon solvent isperchlorethylenc.

8. The method of claim 5, wherein the ester is isopropyl acetate.

9. The method ofclaim 5, wherein the ester is an aliphatic esterprepared from an aliphatic carboxylic acid having less than six carbonatoms andan aliphatic alcohol having less than sit carbon atoms.

- WILBUR H. PETERING.

ADAM G. AI'I'CBIBON.

